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Polyamide filament and industrial fabric using the polyamide filamentRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, Solid Polymer Derived From At Least One Carboxylic Acid Or Derivative, Solid Polymer Derived From At Least One Lactam; From An Amino Carboxylic Acid Or Derivative; Or From A Polycarboxylic Acid Or Derivative, Solid Polymer Derived From An Amino Carboxylic Acid Or Derivative; From A Polyamine And A Polycarboxylic Acid Or Derivative; From At Least One Lactam; Or From A Polyamine Salt Of A Polycarboxylic Acid, Mixed With Additional Polycarboxylic Acid And A Polyamine; Amino Carboxylic Acid Or Derivative; Polyamine Salt Of A Polycarboxylic Acid; Lactam; Or Polymer Derived TherefromPolyamide filament and industrial fabric using the polyamide filament description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060106176, Polyamide filament and industrial fabric using the polyamide filament. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a polyamide filament used for industrial fabric, which filament is obtained by mixing certain amounts of specified two polyamides and does not reduce its thermal contraction stress even by cooling to room temperature after heating; and an industrial fabric using this filament. The industrial fabric obtained using the filament is excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, weaving strength, dimensional stability, running stability, fibrillation resistance, wear resistance, resistance to moist heat, heat resistance, and chemical resistance and is stable without causing misalignment of constituent yarns; and is suited for papermaking fabric, filter cloth of a dehydrator or conveyer belt. BACKGROUND OF THE INVENTION [0002] Fabrics obtained by weaving, as warps and wefts, monofilaments made of a synthetic resin have conventionally been used widely as an industrial fabric. They are, for example, used in various fields including papermaking fabrics, filter cloths and conveyor belts and are required to have fabric properties suited for the intended use or using environment. Of these fabrics, a papermaking fabric used in a papermaking step such as removal of water from raw materials by making use of the network of the fabric must satisfy severe requirements. There is therefore a demand for the development of fabrics which are equipped with fabric rigidity such as diagonal rigidity and flexural rigidity, dimensional stability and wear resistance high enough to permit preferable use under severe environments; and can maintain conditions necessary for making good paper for a prolonged period of time. In addition, surface property, fiber supporting property, improvement in a papermaking yield, good water drainage property and running stability are required. In recent years, owing to the speed-up of a papermaking machine, requirements for papermaking wires become severe further. [0003] Since most of the demands for industrial fabrics and solutions thereof can be understood if papermaking fabrics on which the most severe demand is imposed among industrial fabrics will be described, the present invention will hereinafter be described by using a papermaking fabric as a representative example. [0004] Physical properties which a papermaking fabric must have include rigidity, dimensional stability, wear resistance, surface property, fiber supporting property, improved yield of raw materials for paper manufacture, good water drainage property and running stability. A variety of studies on the fabric design, quality of yarns and weaving conditions and trial production based on such studies have been performed in order to satisfy such requirements. Among factors having a great influence on the physical properties of a fabric, yarns constituting a fabric are important so that researchers have carried out an extensive investigation on their main components, additives, mixing ratio, and characteristics of yarns. [0005] In Japanese Patent Laid-Open Publication No. 2000-144531, disclosed is a polyamide monofilament excellent in wear resistance and heat set property and an industrial cloth which is obtained using the polyamide monofilament and is capable of retaining the woven surface stably with firm knuckle portions. This invention relates to a monofilament obtained by copolymerizing two polyamides. It has characteristics in its components, mixing ratio, concentration of an amide group and melt viscosity. [0006] The polyamide monofilament disclosed in the above-described invention has a wet/dry tensile strength ratio of 85% or greater, a wet/dry flexural rigidity ratio of 55% or greater, maximum longitudinal dimensional change of 4% or less due to moisture absorption or desorption, and a heat set tension ratio, as expressed by a ratio of a yarn tension at normal temperature to a yarn tension prior to heat treatment when the monofilament is heat set at a temperature of from 100.degree. C. to the melting point under tension and then cooled as is, of 2 times or greater. According to this document, the polyamide monofilament therefore does not lose excellent characteristics of polyamide such as wear resistance, has only a small difference in the characteristics between dry time and wet time, can undergo thermal correction easily even in a fiber state because of excellent heat set property, and maintain a stable woven surface because a firm knuckle portion prevents misalignment of constituent yarns during use. The above-described values of the physical properties of this polyamide monofilament such as wet/dry tensile strength ratio, wet/dry flexural rigidity ratio, the maximum longitudinal dimensional change due to moisture absorption or desorption, and heat set tension ratio are however not special but similar to those of conventional polyamide monofilaments or copolymerized polyamide monofilaments. In particular, it is known that Nylon 6 also shows a heat set tension ratio of two times or greater, and it has the maximum dimensional change of 4% or less. Moreover, even if the monofilament has a high wet/dry rigidity and improved heat set tension ratio, it does not mean that an industrial fabric obtained using it has a firm knuckle portion and becomes stable without misalignment of constituent yarns upon use. [0007] Thus, even if the polyamide monofilament has such a novel constitution, fabrics obtained by weaving it are not worth using as an industrial fabric when they cannot have physical properties suited for the intended industrial fabric. Moreover, it is difficult for the fabric as disclosed by the above-described patent document to satisfy the properties required for an industrial fabric such as fabric rigidity such as diagonal rigidity and flexural rigidity, dimensional stability, wear resistance, surface property and running stability. [0008] An object of the present invention is to provide an industrial fabric excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, weaving strength, dimensional stability, running stability, fibrillation resistance, wear resistance, resistance to moist heat, heat resistance, and chemical resistance and is stable without causing misalignment of constituent yarns: and a constituent yarn of the fabric. [0009] In the present invention, a polyamide obtained by polycondensation reaction between metaxylenediamine and adipic acid is called "Polyamide (A)", while another polyamide is called "Polyamide (B)". A yarn composed of a polyamide obtained by mixing from 5 to 50 wt. % of Polyamide (A) with from 95 to 50 wt. % of Polyamide (B) is called "polyamide filament (M)". [0010] The present invention relates to a polyamide filament used for an industrial fabric, which comprises a polyamide resin composition obtained by mixing from 5 to 50 wt. % of a crystalline polyamide (A) obtained by polycondensation reaction of metaxylenediamine and adipic acid and from 95 to 50 wt. % of another polyamide (B). After heating (to 160 to 200.degree. C.) under a constant length condition (at an initial load of 20 mg/d), the filament does not reduce a thermal contraction stress thereof in a cool-down region not greater than 80.degree. C. The polyamide filament may be a monofilament or multifilament. The polyamide (B) may be any one of Polyamide 6, Polyamide 66, Polyamide 610, Polyamide 612 and a polyamide copolymer or a mixture of two or more thereof. From 20 to 40 wt. % of the crystalline polyamide (A) may be mixed with from 80 to 60 wt. % of the another polyamide (B). The polyamide filament as described above may be used as at least a portion of wefts and warps of an industrial fabric. [0011] The present invention relates to a polyamide filament obtained by mixing predetermined amounts of specified two polyamides and does not reduce its thermal contraction stress by cooling to room temperature after heating; and an industrial fabric using this filament as a constituent yarn of the fabric. This fabric is excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, weaving strength, dimensional stability, running stability, fibrillation resistance, wear resistance, resistance to moist heat, heat resistance, and chemical resistance and is stable without causing misalignment of constituent yarns; and is suited for papermaking fabric, filter cloth of a dehydrator or conveyer belt. BRIEF DESCRIPTION OF THE DRAWING [0012] The drawing figure is a graph showing a thermal contraction stress of several polyamide monofilaments. DETAILED DESCRIPTION OF THE INVENTION [0013] In order to overcome the above-described problem, provided in the present invention are: a polyamide filament (M) which is obtained by mixing from 5 to 50 wt. % of a crystalline polyamide (A) prepared by polycondensation reaction between metaxylenediamine and adipic acid and from 95 to 50 wt. % of another polyamide (B), and after heating (to 160 to 200.degree. C.) under a constant length condition (at initial load: 20 mg/d), does not undergo a reduction in its thermal contraction stress in a cool-down region not greater than 80.degree. C.; and an industrial fabric using the polyamide filament (M) as at least a portion of warps and wefts. The fabric obtained according to the present invention is excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, dimensional stability, running stability, wear resistance, resistance to moist heat, fibrillation resistance, and chemical resistance and is stable without causing misalignment of constituent yarns. [0014] The crystalline polyamide (A) available by the polycondensation reaction of metaxylenediamine and adipic acid and usable in the present invention is excellent in hydrolysis resistance, resistance to moist heat, resistance to dry heat and wear resistance and features high strength and high rigidity. The another polyamide (B) is, for example, Polyamide 6, Polyamide 66, Polyamide 610 and Polyamide 612, and copolymer of polyamide, polyamide obtained by mixing one or more than one polyamides and it is excellent in wear resistance and shower resistance. [0015] For the polyamide filament (M) which is a constituent yarn of the present invention, a mixing ratio of the crystalline polyamide (A) and another polyamide (B) is an important factor. When the amount of the crystalline polyamide (A) exceeds 50 wt. %, the polyamide (A) which is stiff and has weak fibrillation resistance serves as sea in the sea-island structure so that the resulting filament has physical properties influenced greatly by the rigidity of the crystalline polyamide (A) and has deteriorated fibrillation resistance. Such a filament sometimes cracks by the contact with a foil or the like or a high-pressure shower. [0016] When the amount of the crystalline polyamide (A) is less than 5 wt. %, the resulting filament becomes a filament not suited for industrial fabric because of deteriorations in heat resistance, dry heat resistance, chemical resistance and abrasion resistance. As a result of extensive investigation by the present inventor, a polyamide filament obtained by mixing from 5 to 50 wt. % of a crystalline polyamide (A) prepared by polycondensation reaction between metaxylenediamine and adipic acid and from 95 to 50 wt. % of another polyamide (B) satisfies the object of the present invention. A filament obtained by mixing from 20 to 40 wt. % of a crystalline polyamide (A) and from 80 to 60 wt. % of another polyamide (B) is more preferred. [0017] The polyamide filament (M) is a filament equipped with a special physical property, that is, when the filament is cooled after heating (to 160 to 200.degree. C.) under a constant length condition (at an initial load of 20 mg/d), it does not reduce its thermal contraction stress in a cool-down region not greater than 80.degree. C. In other words, it has a thermal contraction stress which increases or is fixed at a temperature not greater than 80.degree. C. In general, industrial fabric is heat set to about 160 to 200.degree. C. after weaving in order to form a knuckle at the intersections between yarns, thereby stabilizing the attitude of the fabric. Without heating, the yarns constituting the fabric are only crossed each other and misalignment occurs, which leads to a sleazy fabric. In the filaments made of a synthetic resin, at intersections between warps and wefts, knuckles in the form following their shapes are formed in order to get tangle warps and wefts by heating. The thermal contraction stress increases by heating and owing to a tension thus produced, yarns thus crossed each other are tangled more strongly, whereby the fabric is able to have a stable attitude as a whole. Polyester monofilaments which have excellent rigidity and dimensional stability and therefore are suited for an industrial fabric hardly undergo a reduction in a thermal contraction stress during cooling. When they are heat set once, knuckles are formed firmly even under normal temperature and any problem such as misalignment of constituent yarns and bow of fabric does not occur. Although industrial fabrics made of only polyester monofilaments have been used, many fabrics are obtained by weaving polyester monofilaments and polyamide monofilaments in order to impart them with improved wear resistance and impact resistance. [0018] Ordinary union fabrics are not completely satisfactory as an industrial fabric because rigidity and dimensional stability lower owing to water absorption of polyamide monofilaments. Different from polyester monofilaments, polyamide monofilaments tend to cause misalignment of constituent yarns even after heat setting and the resulting fabric inevitably becomes sleazy. In ordinary polyamide monofilaments, at intersections between warps and wefts, knuckles in the form following their shapes are formed in order to get tangle warps and wefts by heating. The thermal contraction stress increases by heating and owing to a tension thus produced, yarns thus crossed each other are tangled more strongly, whereby the fabric is able to have a stable attitude as a whole. After heat setting, however, the thermal contraction stress gradually lowers during a cooling step, which leads to a reduction in the tension of wefts and warps which have been interwoven strongly when the temperature is high. For example, Nylon 6, Nylon 610 or Nylon 6/Nylon 66 copolymer nylon shows the highest thermal contraction stress at about 160 to 200.degree. C. and this thermal contraction stress decreases by subsequent cooling. In particular, Nylon 610 shows a marked decrease in contraction stress. In other words, an industrial fabric obtained by weaving such polyamide monofilaments, knuckles once formed by heat setting become loose and a space appears between yarns, which have been crossed each other, by a reduction in the thermal contraction stress, resulting in a fabric with misalignment or shift of yarns. Even if polyamide monofilaments are woven with polyester monofilaments, their reduction in thermal contraction stress cannot be overcome. [0019] In the present invention, after heating, the polyamide filament (M) which is a constituent yarn of a woven fabric does not undergo a reduction in thermal contraction stress in a cool-down region not greater than 80.degree. C. so that an industrial fabric excellent in diagonal rigidity and flexural rigidity and stable without causing misalignment of constituent yarns can be obtained. [0020] In the fabric of the present invention, the above-described polyamide filament may be used as at least a portion of constituent yarns of the fabric. It can be used as some or all of wefts and warps. In general, it is preferred to use as wefts instead of a polyamide which is required to have wear resistance and shower resistance. It can also be woven with a polyester filament which hardly undergoes a reduction in thermal contraction stress during cooling. This makes it possible to manufacture a fabric which easily causes neither misalignment of constituent yarns nor bow of fabric and is excellent in diagonal rigidity, flexural rigidity, dimensional stability, running stability, wear resistance, moist heat resistance, dry heat resistance, fibrillation resistance and chemical resistance. Continue reading about Polyamide filament and industrial fabric using the polyamide filament... 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